The invention relates to drives operated by a sequence of pulses, and more particularly to such a drive comprising a control circuit and a motor operated thereby, in which the desired motion of the motor is represented by a chain of pulses of which each pulse is representative of an incremental displacement of the motor.
Known drives of this sort make use of a stepper motor and the control circuit serves to convert a control pulse train into a power pulse train supplied to the stepper motor. In response to each incoming power pulse the stepper motor turns through a given angle so that the true position of the motor is to be dictated by the sum of all the control pulses received.
If varying loads have to be driven by the stepper motors of such known drives it may happen that when the load torque is particularly high the stepper motor fails to completely respond to a power pulse and is not advanced by one step into the next angular position but drops back into the previous one. Such a case may for example occur if the part moved by the stepper motor runs skew in its guide or otherwise jams. If a control pulse is "lost" in this manner, the true position of the stepper motor will from then on no longer tally with the position assumed by the computer or the like on the basis of the number of pulses sent to the motor.
In order to move heavy loads with time-dependent fluctuations, other types of motors such as DC motors or compressed air motors are well suited, which are able to supply very high torques or linear forces. However, such motors functioning in an analog or continuous manner have not so far been able to be operated by simple chains of pulses like stepper motors.